Thermionic valves



July 2, 1963 N. E. H. PEARSON 3,

THERMIONIC VALVES Filed March 11, 1960 United States Patent 3,096,459 THERMIQNIC VALVES Norman Edward Hugo Pearson, Enlield, England, as-

signor to Associated Electrical Industries Limited, London, England, a British company Filed Mar. 11, 1960, Ser. No. 14,456 Claims priority, application Great Britain Mar. 13, 1959 2 Claims. (61. 313-241) This invention relates to thermionic valves and has an important application in thermionic valves having a top anode connection.

It is common practice in thermionic valves to have an insulating disc at the upper end usually of mica which is apertured to hold the upper ends of the electrodes in proper spaced relationship.

During the operation of such a valve it has been found that some errant electrons from the cathode reach the getter deposit, the top cap and the other components apart from the anode which are at anode potential and pass into the anode circuit of the valve. Others bombard the glass walls of the bulb and set up accumulations of charge on the walls. These charge accumulations, it is believed, discharge themselves erratically to the getter deposit and thence into the anode circuit. Since the rate of discharge is far from steady something in the nature of a noise voltage is capacity coupled to the control grid of the valve. This is obviously undesirable and, when it occurs in a valve such as a line output beam tetrode in a television receiver for example, may cause erratic firing of the line oscillator.

In a standard valve, electrons will reach the bulb walls via the small gap between the top of the beam plate and the underside of the mica and also between the top of the anode and the underside of the mica. Others pass upwards through such holes in the mica as the small gaps around the grid support rods and the cathode tube where these are fitted into the mica and also through leakage slots in the mica. By leakage slots is meant slots so positioned in the mica as to lengthen the leakage path across the mica surfaces between the various components of the electrode structure which either pass through or are in electrical connection with supporting rods which pass through the mica.

The main object of the invention is to avoid or minimise these disadvantages.

According to the present invention a thermionic valve comprises electrodes extending between upper and lower insulating cross plates and with the ends of the electrodes fitting into apertures in the plates, a surrounding envelope, a top anode connection mounted in the upper end of the envelope, together with a metallic shield mounted on the top face of the upper insulating plate and extending over the ends of the electrodes so as to screen the upper end of the valve envelope against electrons escaping through the apertures in the insulating plate.

Preferably the metallic shield is of an inverted box like structure with the edges of the opening abutting against the insulating plate and is connected to the cathode of the valve or to earth to prevent the accumulation of charge on the shield.

The term upper and lower as employed herein refers to the conditions obtaining when the valve is positioned to extend vertically upwards from a base but they do not imply that the valve will always be used in such a position.

The invention is applicable both to diodes and to valves having auxiliary electrodes, e.g. grids.

In order that the invention may be more clearly understood reference will now be made to the accompanying drawings which show the invention applied to a tetrode suitable as a television line output valve,

FIG. 1 showing the general assembly, and

FIG. 2 being an exploded view of the shield and mica plate.

In the drawing the reference 1 indicates the valve envelope and 2 is a mica plate locating the upper ends of the electrodes. 3 is the anode connected to a top anode terminal 4 and 5 represents the gettering disc. The electrode assembly also includes a control grid 6 and a beam plate 7. The invention consists in mounting a box-like shield of sheet metal on the top of the mica plate 2.

In the actual arrangement shown the beam plate 7 is formed with lugs 9, l0 and 11 extending through the mica plate and the shield 8 is held by these lugs, whilst the lug 9 is engaged by a lug 12 on the end of the shield.

As will be seen from the drawing, the box-like shield envelops the tops of the grid rods and provides a physical barrier to electrons passing through the mica in this region. The long sides of the shield are further provided with extensions 13 which project downwards through the mica and which remain in contact with the inside of the beam plate. These extensions 13 seal off much of the gap between the top of the anode and the underside of the mica and thus at least minimise the escape of electrons from here.

What I claim is:

l. A thermionic valve comprising at least an anode and a grid electrode, upper and lower insulating cross plates apertured to support the ends of the electrodes, a surrounding envelope, a top anode connection mounted in the upper end of the envelope, a beam plate extending longitudinally of said envelope and having at its upper end spaced lugs projecting through and above apertures in said upper insulating plate, and a metallic shield mounted on the top face of the upper insulating plate and extending over the ends of the electrodes so as to screen the upper end of the valve envelope against electrons escaping through the apertures in the insulating plate, said metallic shield comprising an inverted box formed with top and side walls having edges abutting against the upper insulating plate said lugs engaging the side walls of said shield to hold said shield in place on said upper plate with said shield having at least one side projection extending down through an aperture in said upper insulating plate and into engagement with said beam plate below said upper insulating plate.

2. An electrical thermionic beam valve comprising an anode, a cathode and a grid electrode, upper and lower insulating cross plates apertured to supportingly receive the ends of the electrodes, a surrounding envelope, beam plates mounted for shielding the gaps between the edges of the anode and cathode, a top anode connection mounted in the upper end of the envelope, a metallic electron shield mounted on the top face of the upper insulating plate and extending over the ends of the electrodes so as to screen the upper end of the valve envelope against free electrons escaping through the apertures in the insulating plate, said metallic shield comprising an openended inverted box having side and top walls forming continuous wall surfaces, and tags extending from the edges of said side walls, which tags extend transversely through the upper insulating plate and beyond the underside thereof to prevent electrons escaping across the under side of the insulating plate, the portions of said tags projecting from the underside of said upper insulating plate being in abutting contact with said beam plates.

References Cited in the file of this patent UNITED STATES PATENTS 1,936,187 Denzler Nov. 21, 1933 2,016,649 Parker Oct. 8, 1935 2,017,549 Salzberg Oct. 15, 1935 2,227,093 Laico Dec. 31, 1940 2,705,294 Shrader Mar. 29, 1955 

1. A THERMIONIC VALVE COMPRISING AT LEAST AN ANODE AND A GRID ELECTRODE, UPPER AND LOWER INSULATING CROSS PLATES APERTURED TO SUPPORT THE ENDS OF THE ELECTRODES, A SURROUNDING ENVELOPE, A TOP ANODE CONNECTION MOUNTED IN THE UPPER END OF THE ENVELOPE, A BEAM PLATE EXTENDING LONGITUDINALLY OF SAID ENVELOPE AND HAVING AT ITS UPPER END SPACED LUGS PROJECTING THROUGH AND ABOVE APERTURES IN SAID UPPER INSULATING PLATE, AND A METALLIC SHIELD MOUNTED ON THE TOP FACE OF THE UPPER INSULATING PLATE AND EXTENDING OVER THE ENDS OF THE ELECTRODES SO AS TO SCREEN THE UPPER END OF THE VALVE ENVELOPE AGAINST ELECTRONS ESCAPING THROUGH THE APERTURES IN THE INSULATING PLATE, SAID METALLIC SHIELD COMPRISING AN INVERTED BOX FORMED WITH TOP AND SIDE WALL HAVING EDGES ABUTTING AGAINST THE UPPER INSULATING PLATE SAID LUGS ENGAGING THE SIDE WALLS OF SAID SHIELD TO HOLD SAID SHIELD IN PLACE ON SAID UPPER PLATE WITH SAID SHIELD HAVING AT LEAST ONE SIDE PROJECTION EXTENDING DOWN THROUGH AN APERTURE IN SAID UPPER INSULATING PLATE AND INTO ENGAGEMENT WITH SAID BEAM PLATE BELOW SAID UPPER UNSULATING PLATE. 